An ultrasonic transducer that transmits and receives ultrasonic waves is used in a diagnosis for a tumor and the like in a human body or in a nondestructive inspection and the like for a structure.
There has been used so far an ultrasonic transducer using oscillation of a piezoelectric body. However, with the development of the recent MEMS technology, a CMUT (Capacitive Micromachined Ultrasonic Transducer) in which an oscillation unit is formed on a silicon substrate has been actively developed in an effort to realize practical use.
U.S. Pat. No. 6,320,239B1 (Patent Literature 1) discloses a single CMUT and those arranged in array.
Each of U.S. Pat. No. 6,571,445B2 (Patent Literature 2) and U.S. Pat. No. 6,562,650B2 (Patent Literature 3) discloses a technique of forming a CMUT on a signal processing circuit formed on a silicon substrate.
U.S. Pat. No. 6,430,109B1 (Patent Literature 4) discloses a technique of supplying an electric signal to a bottom electrode of a CMUT formed on a silicon substrate by providing a hole penetrating the silicon substrate.